Method of inhibiting corrosion



United States Patent ABSTRACT OF THE DISCLOSURE Use of certain thiuronium compounds to inhibit corrosion of ferrous metals exposed to aqueous systems containing hydrochloric acid, hydrogen sulfide, carbon dioxide or mixtures thereof. An illustrative thiuronium compound is bis (isothiureidomethyl) dodecylbenzene dihydrochloride.

The present invention relates to a method of inhibiting corrosion of ferrous metals exposed to aqueous systems containing hydrochloric acid, hydrogen sulfide, carbon dioxide or mixtures thereof. More particularly, the present invention relates to a method of inhibiting corrosion of the aforementioned type through the use of certain thiuronium compounds.

It is well known that exposure of ferrous metals to aqueous systems results in corrosion of the metals. This is particularly true when the aqueous systems contain appreciable amounts of hydrogen chloride, hydrogen sulfide, carbon dioxide, or mixture of these materials. One means of alleviating this type of corrosion is by adding to the aqueous systems various chemical compounds. Many chemicals are known which inhibit the corrosion of ferrous metals which are exposed to aqueous systems containing hydrogen chloride, hydrogen sulfide, or carbon dioxidepIt is highly desirable for those working in this field to have available chemical compounds which are effective at low concentrations (e.g., less than 100 parts per million). It is also highly desirable for those working in this field to have available a number of chemical compounds which are suitable as inhibitors. This is particularly true, since the economics may change and a corrosion inhibitor, once considered uneconomical, is then economical to use. Also, a choice of inhibitors give those working in this field a choice of suppliers.

It is an object of the present invention to provide an improvement in the means of inhibiting corrosion through the use of certain corrosion inhibitors of improved efiiciency.

It is another object of the invention to provide an im proved method of inhibiting corrosion of ferrous metals in contact with aqueous systems containing hydrochloric acid, hydrogen sulfide, carbon dioxide or mixtures thereof.

It is a particular object of the invention to inhibit corrosion of the type described above through the use of certain thiuronium compounds.

Broadly stated the present invention relates to a method of inhibiting corrosion of ferrous metals in contact with aqueous systems containing hydrogen sulfide hydrogen chloride, carbon dioxide, or mixtures thereof, wherein the method comprises adding to the aqueous system, a corrosion-inhibiting amount of a thiuronium compound represented by the formula 3,457,030 Patented July 22, 1969 ice wherein R is an alkyl group, either branched or straight chain, containing from 6 to 18 carbon atoms, wherein A is either hydrogen or a methyl group, wherein X is a halogen, which, preferably, is chlorine, and wherein n is a number of from about 1 to about 2.8.

Preferably, the method of our invention uses a thiuronium compound represented by the formula wherein R is an alkyl group, either branched or straight chain, containing from about 10 to about 18 carbon atoms, preferably from about 10 to about 14 carbon atoms, wherein A is either hydrogen or a methyl group, wherein X is a halogen, which, preferably, is chlorine, and wherein n is a number of from about 1.4 to about 2.8, preferably from about 1.6 to about 2.4. For convenience, compounds wherein n is from about 1.4 to about 2.8 are referred to as bis thiuronium compounds.

More preferably, the method of our invention relates to a method of inhibiting corrosion of ferrous metals in contact with aqueous systems containing hydrogen sulfide, wherein the method comprises adding to the aqueous system a corrosion-inhibiting amount of a bis thiuronium compound as described immediately above.

Examples of suitable thiuronium compounds for use in the method of our invention have the formula wherein R, A, X and n are as follows:

R A X n n-Cs-Crs (mixed Cl 1. 0 bf-Ca-C13 (mixed) Cl 1. 2 nC-C1s (mixed) H 131 1. 4 br-Cs-Cm (mixed)- H I l. 6 n-Ca-Cm (rmxed) CH3 Cl 1. 8 bl-Cs-Cm (mixed) CH3 Cl 2. O Il-Ca-Cm (milfed) CH3 B1 2. 2 br-CrC (mixed) CH Br 2. 4 11-05.- H Cl 2. 6 n-C H C1 2. 8 H 01 2. 0

H Cl 2. 4

H Cl 2. 2

...... CH3 Cl 2. O

CH3 I 1. 8

CH3 C1 1. 6

CH Cl 1. 4

CH3 Cl 1. 2

H Cl 1. 4

H Cl 1. 6

H Br 1. 8

H Br 2. 0

CH Cl 2. 4

CH Br 2. 8

H Cl 1. 6

H Cl 1. 8

H C1 2. O

CH3 Cl 2. 4

CH3 Cl 2. 6

CH3 Cl 2. 8

CH Cl 1. 8

- CH Cl 1. 6

n-CwC1s(mixed)* H Cl 1.6 br-CmC a (mixed)* H Cl 1. 8

The asterisk indicates that these particular compounds are preferred. The term n refers to straight chain; the term hr to branched chain. The term mixed means that alkyl groups of varying chain length are present.

Inasmuch as the alkylaromatic portion of the thiuronium compounds of our invention is an important feature of our invention, this will be described in considerable detail. The aromatic radical of the compounds of our invention is derived from either benzene or toluene, but preferably is derived from benzene. The long chain alkyl group of the alkylaromatic portion of the thiuronium compounds of our invention can be either straight or branched chain, and contains from about 6 to about 18 carbon atoms. Usually, the alkyl group contains from 10 to 18 carbon atoms, but preferably contains from 10 to 14 carbon atoms. The thiuronium compounds can be derived from a single alkylaromatic compound (e.g., hexylbenzene, octylbenzene, decylbenzene, etc.). More usually, the thiuronium compounds are derived from mixtures of alkylaromatic hydrocarbons containing alkyl groups of varying lengths, as hereinbefore defined. In fact, the more suitable commercially available alkylaromatic hydrocarbons are mixtures.

An example of a particularly suitable commercially available alkylaromatic hydrocarbon which can be used to prepare the corrosion inhibitors of our invention is a material which is known to the trade as dodecylbenzene. Dodecylbenzene is available under the trade name of Neolene 400 from Continental Oil Company. In a typical process dodecylbenzene is prepared by first polymerizing propylene to produce a mixture of olefins which are predominantly C (dodecene). Benzene is then alkylated with the dodecene to produce dodecylbenzene. The preparation of dodecylbenzene is described more completely in US. Patent 2,941,015 to Robert R. Kylander,

which patent is made a part of this specification. A typical sample of dodecylbenzene has the following properties:

Distillation range, F.:

Refractive index, 25 C. 1.4885 Appearance, clear and water white Flash point (closed cup), F. 260 Viscosity, centipoises:

1 Cryogenic method using benzene. ASTM D 611.

3 ASTM. D1159.

" ASTM D--156.

ASTM D-56.

It is generally known that the alkyl group in dodecylbenzene is branched chain. More recently, in order to produce detergents which are less resistant to attack by bacteria, straight chain alkylaromatic hydrocarbons, similar to dodecylbenzene, have been prepared. These materials constitute a class of materials which, when sulfonated, are known in industry as biodegradable detergents. It is to be understood that any of the n-alkylaromatic hydrocarbons which are used in preparing biodegradable detergents and having at least 10 carbon atoms in the alkyl group can be used to prepare the corrosion inhibitors of our invention.

The preparation of a particularly suitable n-alkylaromatic hydrocarbon for use in our invention is described in application Ser. No. 129,252, filed Aug. 4, 1961, and now abandoned, and having the same assignee as the present application. For reason of convenience, this application is made a part of the present application. Briefly, application Ser. No. 129,252 relates to a process of preparing a detergent alkylate wherein the process comprises the following steps, broadly stated: (a) separating a fraction of substantially straight chain C C hydrocarbons from a petroleum distillate substantially free of olefins and containing said straight chain hydrocarbons together with non-straight chain hydrocarbons, (b) chlorinating said fraction to the extent whereby between about 10 and about 35 mole percent of the straight chain hydrocarbons present are substantially only monochlorinated, (c) alkylating an aromatic compound, selected from the group consisting of benzene, a lower alkyl substituted benzene and mixtures thereof, with the chlorination product of step (b) in the presence of an alkylation catalyst.

n-Alkylaromatic hydrocarbons of the aforementioned type are available under the trademarks Nalkylene 500 and Nalkylens 600 from Continental Oil Company. These materials have the following typical properties:

NALKYLEN'E 500 Color-Saybolt. Specific gravity (20/20)-.- Viscosity (Saybolt scco11ds).-

NALKYLENE" (300 Boiling range F.):

580-590 ASTM D-447. 95% 5 BromineNo 0.05 max RM. No. 21. Average molecular weight. Color-Saybolt Specific gravity Viscosity (Saybolt seconds) Still another suitable alkylaromatic hydrocarbon for use in preparing the corrosion inhibitor of our invention is a byproduct of the production of a material which we refer to as dimer alkylate. Dimer alkylate has branched-chain alkyl groups, as does dodecylbenzene. Briefly described, dimer alkylate is prepared by the following steps:

(1) dimerization of a suitable feedstock, such as cat poly gasoline, and

(2) alkylation of an aromatic hydrocarbon with the dimer formed in step (1).

DESCRIPTION OF PREPARATION OF THIURONIUM COMPOUNDS The first step in preparing the thiuronium compounds of our invention is the preparation of a halomethylated alkylaromatic hydrocarbon (preferably (bis chloromethylated alkylaromatic hydrocarbon). In one method these materials are prepared by using a chloromethylating agent which is formed by reacting formaldehyde or a compound which engenders formaldehyde with a chlorine-containing compound which will engender hydrogen chloride in the presence of an alcohol and sulfuric acid. In addition to chloromethylating agents it is possible to use halomethylating agents which contain other halogens, such as bromine or iodine, which are prepared in a similar manner.

Suitable chlorine-containing compounds which will engender hydrogen chloride under the conditions used herein include phosphorus trichloride, phosphorus pentachloride, sulfuric joxychloride, sulfurous oxychloride, and acyl chlorides such as acetyl chloride. Suitable alcohols are the primary monatomic saturated aliphatic alcohols containing from 1 to 4 carbon atoms, such as, for example, methanol, ethanol, normal propanol and normal butanol.

The relative amounts of the various components of the chloromethylating reagent, and the amount of chloromethylating agent used in relation to the alkaryl hydrocarbon, are shown below.

Suitable Preferred (moles) (moles) Alkaryl hydrocarbon 1 1 Formaldehyde 2. 1-4. 0 3. 4-3. 6 A 2. 1-4. 0 3. 2-3. 4 in g compound (e PO1 1. 0-3.0 1.1-1.3

Sulfuric acid 2. 6-6. 0 4. 0-5. 0

preparation of a monohalomethylated alkylaromatic hydrocarbon: 200 grams of dodecylbenzene is treated with a chloromethylating mixture which has been prepared as follows: 42 grams of p-formaldehyde and 43 grams methyl alcohol are added to a 1-liter Morton flask which is equipped with a sealed stirrer, thermometer, and dropping funnel. The fiask is placed in an ice bath and mixing is begun. Phosphorus trichloride (65.5 grams) is added dropwise from the funnel while maintaining a temperature between 29 and 32 C. After the chloride addition, the reaction mass is aged 10 minutes at the same temperature. One hundred seventy-five grams of percent sulfuric acid is then added to the dropping funnel. The sulfuric acid is then added to the reaction mass at a rate to maintain the same temperature. This is followed by post-stirring for an additional 15 minutes. This reaction mass and the dodecylbenzene are combined and heated at 52-55 C. for 3 hours to produce the chloromethylated dodecylbenzene.

The preparation of the his halomethylated alkylaromatic hydrocarbon is similar to the preceding, with the exception that 100 grams of alkylaromatic hydrocarbon is used and the time and temperature are 5 hours and 67 C., respectively.

With regard to the bis halomethylated products, they are mixtures of homologous products containing 1, 2 or 3 halomethyl groups. Moreover, the distribution of these products varies according to the type of alkylaromatic hydrocarbon employed. Thus, while the above-identified Neolene 400 and Nalkylene 500 exhibit approximately equal reactivity in a dihalomethylation process, the product of the former is essentially all his derivative, whereas the product of the latter is more nearly a mixture of mono and tris derivatives.

The degree of halomethylation is the average of the number of halomethyl groups present. As indicated previously, for reason of convenience we refer to those compounds derived from materials having from about 1.4 to about 2.8 halomethyl groups, preferably from about 1.6 to about 2.4 halomethyl groups, as bis compounds.

The second step in the process of preparing the corrosion inhibitors of our invention comprises reacting the halomethylated alkylaromatic hydrocarbon with thiourea. The reaction is generally carried out in the presence of an inert volatile organic solvent (e.g., isopropanol). Since the reaction of the second step is well known to those skilled in the art, it is believed that further description is unnecessary.

The thiuronium compounds in some instances can suitably be used as corrosion inhibitors in concentrations as low as 2 parts per million (by weight) based on the aqueous solution in which it is used. More suitably, the thiuronium compounds are used in a concentration of at least 10 parts per million. Preferably, they are used in a concentration of at least 50 parts per million. The bis thiuronium compounds are more effective than the monothiuronium compound. In addition, the effectiveness of the bis thiuronium compounds varies slightly depending on the nature of the alkylaromatic portion.

In order to disclose the nature of the present invention still more clearly, the following illustrative examples will be given. It is to be understood that the invention is not to be limited to the specific conditions or details set forth in these examples except in so far as such limitations are specified in the appended claims.

Example 1 Using the procedure described hereinbefore, and using commercial dodecylbenzene as the alkylaromatic hydrocarbon, the monothiuronium compounds was prepared. (This material is referred to as Compound A in the table below.) Similarly, using hexylbenzene as the alkylaromatic hydrocarbon, the monothiuronium compound was prepared. (This material is referred to as Compound B in the table below.)

7 Example 2 The compounds described in Example 1 were subjected to the following tests: 10 percent aqueous HCl solution, 3.8 percent aqueous HCl solution, aqueous hydrogen sulfide solution, and aqueous carbon dioxide solution.

The tests were made using S.A.E.-type 1020 mild steel coupons, 1 inch by 3 inch by inch. The surfaces of the coupons were prepared on a water-cooled surface grinder using a number 46 grit wheel. The coupons were washed in acetone after grinding, air dried, and then were stored in a vacuum dessicator until needed.

The 10 percent HCl and 3.8 percent HCl tests were made in 250 ml. beakers, capped with water glass covers, which contained 200 ml. of test solution.

The H 8 and CO tests were conducted in pressure bottles containing 150 ml. of percent NaCl, 50 ml. of kerosene plus the thiuronium compound. The H 5 and CO gases were bubbled into the bottom' of each bottle through a glass tube fitted in a rubber stopper.

A stock solution of each of the thiuronium compounds was prepared to contain 50,000 p.p.m. of the compound in methanol. The required amount to give the desired concentration was added to the test vessels.

The coupons were weighed before and after the tests. From the weights the percent protection was calculated.

The results of this series of tests are shown in Table I below.

TABLE I.--PER%ENT PROTECTION AT AMBIENT l Monothiuronium compound derived from dodecylbenzene. 2 Monothiuronium compound derived from hexylbenzene.

Example 3 Nalkylene 500 and chloromethylating reagent (3.4 equivalents) prepared as outlined above were combined and heated 5 hours at 6768 C. The crude product was separated, washed with water, dilute base and subsequently dried. Analysis of the finished product indicated a 94.5 percent yield of chloromethylated alkylbenzene containing- 17.1 weight percent chlorine and having an average of 1.6 chloromethyl groups per molecule. The product was a mixture consisting essentially of mono, bis and tris halomethyl alkylbenzene together with minor amounts of diarylmethane-type condensation products.

Refluxing for 3 hours a solution of the chloromethylated alkylbenzene prepared above, thiourea percent excess) and isopropanol (1 part) produced the corresponding isothiuronium salts in essentially quantitative yield. This material is referred to as compound C in the table below.

Example 4 Dodecylbenzylchloride derived from propylene tetramer was treated 3 hours at 75 C. with 3.4 equivalents of the above-described chloromethylating reagent. After separation, the crude product was subjected to a further identical chloromethylation. Distillation of the second product yielded a 91/9 mixture of bis and mono chloromethyldodecylbenzene (boiling range: ISO-170 C./0.1 mm.) obtained as a viscous water-white liquid.

Refiuxing for 3 hours a solution of 91/9 bis-mono chloride, thiourea (10 percent excess) and isopropanol (1 part) produced the corresponding isothiuronium salts in essentially quantitative yield. This material is referred to as compound D in the table below.

Example 5 Example 6 A mixture of secondary octylbenzenes (0.2 moles) was reacted with one-half unit of chloromcthylating agent for 3 hours at 55 C. The'product contained 21 weight percent chlorine and 1.64 chloromethyl groups per mole.

The isothiuronium derivative was prepared as described in the preceding examples. This isothiuronium derivative is referred to as compound F in the table below.

Example 7 Using the procedure described in Example 2, the materials described inExarnples 3 to 6 above were tested for their elfectiveness as H S corrosion inhibitors. For purposes of comparison the compound 1,3(5-dodeeyl)xylene bis(trimethylammonium) chloride was also tested. The results of this series of tests are shown in Table II below.

TABLE IL-BESULTS OF H 8 CORROSION TESTS Percent Protection by Inhibition Compound 0 D E 3 F 4 G 1 Concentration (p.p.m.):

1 Bis(isothiureidomethyl) dodecylbenzene dihydrchloride, derived from Nalkylene 500-prod t of Example 3.

2 Bis(isothiureidomethyl) odecylbenzeno dihydrochloride, wherein the dodeeene is derived from propylene tetramer-produet of Example 4.

3 Bis(isothiureidomethyl) dodeeyltoluene dihydroehloride, wherein the dodecene is derived from propylene tetramerproduct of Example 5. D Bisqsoghiureidomcthyl)octylbeuzcne dihydrochlorldeproduct ol' xamp e 1,3(5-dodeeyl) xylene bis(trimethylammonium)chloride.

While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto, since many modifications may be made; and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

The invention, having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. The method of inhibiting corrosion of ferrous metals in contact with aqueous systems containing hydrogen chloride, hydrogen sulfide, carbon dioxide, or mixtures thereof, said method comprising adding to the aqueous system a corrosion inhibiting amount of a compound represented by the formula:

NH! n 2. The method of claim 1 wherein the compound has the formula:

/NH H23 C IIX wherein R is an alkyl group containing from about 6 to about 18 carbon atoms, wherein A is selected from the group consisting of hydrogen and a methyl radical, and wherein X is a halogen.

3. The method of claim 1, wherein the compound has the formula:

[0 H28 C\ EX] N H2 n R wherein R is an alkyl group containing from about 10 to about 18 carbon atoms, wherein A is selected from the group consisting of hydrogen and a methyl radical, wherein X is a halogen and wherein n is a number of from about 1.4 to about 2.8.

4. The method of claim 3, characterized further in that X is chlorine.

5. The method of claim 4, characterized further in that n is a number of from about 1.6 to about 2.4.

6. The method of inhibiting corrosion of ferrous metal in contact with aqueous systems containing hydrogen sulfide, said method comprising adding to the aqueous system a corrosion inhibiting amount of a compound represented by the formula:

wherein R is an alkyl group containing from about 10 to about 18 carbon atoms, wherein A is selected from the group consisting of hydrogen and a methyl radical, wherein X is a halogen, and wherein n is a number of from about 1.4 to about 2.8.

7. The method of claim 6, characterized further in that X is chlorine.

8. The method of claim 7, characterized further in that n is a number of from about 1.6 to about 2.4.

9. The method of claim 8, characterized further in that R is an alkyl group containing from about 10 to about 14 carbon atoms.

10. The method of claim 9, characterized further in that A is hydrogen.

References Cited UNITED STATES PATENTS 2,209,464 7/ 1940 Loane et a1. 2,618,603 11/1952 Schaefier 212.5 XR 2,947,703 8/1960 Larsonneur 21-2.5 XR 3,226,180 12/1965 Irwin 212.7 XR 3,260,538 7/1966 Gardner 212.7 XR 3,371,010 2/1968 Hamilton et a1. 260-564 XR OTHER REFERENCES George Holmes Richter: Textbook of Organic Chemistry, third edition, John Wiley & Sons, New York, 1952 (pp. 280-281 relied on), copy in Group 171.

Herbert H. Uhlig: The Corrosion Handbook, John Wiley & Sons, New York, 1948 (p. 910 relied on), copy in Group 171.

MORRIS O. WOLK, Primary Examiner B. S. RICHMAN, Assistant Examiner US. Cl. X.R. 212.5, 58 

